This invention relates to a fuel injection system for small internal combustion engines and more particularly to a fuel injection system having a rotary throttle valve type charge forming device.
Typically, carburetors have been used to supply a fuel and air mixture to both four-stroke and two-stroke small internal combustion engines. For many applications where small two-stroke engines are utilized such as handheld power chain saws, weed trimmers, leaf blowers, garden equipment and the like, carburetors with both a diaphragm fuel delivery pump and a diaphragm fuel metering system have been utilized. In operation, two-stroke engines utilizing these carburetors have a high level of hydrocarbon exhaust emissions which are detrimental to the environment and exceed and cannot meet the exhaust emission requirements imposed by the State of California and the emission requirements proposed by the Environmental Protection Agency of the United States Government and the governments of several other countries.
Due to the relatively low selling price of two-stroke small engines and particularly two-stroke engines for handheld power tools, it is not economically feasible to utilize electronic fuel injection systems such as those typically used for automotive vehicle applications. While various lower cost mechanical fuel injection systems have been proposed for two-stroke small engines, some have either failed to meet the California and proposed emission standards or are economically and/or technically unfeasible for commercial manufacture and sale for two-stroke small engine applications such as handheld power tools.
Fortunately, and incorporated herein by reference, U.S. Pat. No. 6,427,646 has provided a solution to economically reduce the level of hydrocarbon exhaust emissions from a small two-cycle engine by replacing the conventional carburetor with a charge forming device and a tuned injector tube which injects a rich mixture of fuel-and-air for combustion directly into the cylinder of a two-stroke engine, instead of into the crankcase as traditionally designed for lubrication then combustion purposes. The charge forming device of the above reference utilizes a series of butterfly valves to control fuel and air flow, however, this fuel injection system has yet to be applied to a charge forming device having a rotary type throttle valve. Furthermore, at high engine speeds or wide open throttle conditions, a mixture of fuel and lubricating oil, even with the fuel injection system technology, must still be drawn into the crankcase to lubricate bearings and moving parts, but without creating rough idle conditions or high emissions during low speed operation.
A fuel injection system injects a rich mixture of fuel-and-air for combustion directly into a cylinder of a two-cycle engine through an intake port for combustion. A charge forming device of the fuel injection system carries a primary air intake passage which flows air into the crankcase of the engine, and a rich fuel-and-air mixing passage which flows the majority of fuel into the cylinder, preferably via a tuned injector tube. To control air flow through the air intake passage and simultaneously control fuel flow into the fuel-and-air mixing passage, a rotary throttle valve rotateably and axially moveably traverses both passages. A mixture of fuel and oil is drawn into the air intake passage via a fuel bleed passage only during wide open throttle conditions for lubrication of engine moving parts and bearings contained within the crankcase.
A rotary member of the rotary throttle valve seats rotatably and axially movably in a valve chamber which communicates perpendicularly through the air intake passage. A throttle bore extends laterally though the rotary member and aligns with the air intake passage when the rotary throttle valve is rotated to a wide open throttle position, and partially mis-aligns to the air intake passage when the valve is rotated to an idle position. A needle controls fuel flow into the fuel-and-air mixing passage by projecting concentrically from the rotary member and axially into a fuel feed tube which delivers fuel from a fuel metering chamber into the fuel-and-air mixing passage. As the rotary member rotates to control air flow through the air intake passage, the rotary member and the needle move axially so that the end of the needle moves into and out of a fuel nozzle carried by the fuel feed tube to vary fuel flow into the fuel-and-air mixing passage.
Objects, features, and advantages of this invention include a rotary valve type fuel injection system for a two-stroke engine providing significantly decreased engine hydrocarbon exhaust emissions, significantly improved fuel economy, improved engine starting and idle running stability, improved ease, repeatability and stability for calibration and adjustment of the fuel-air ratio and flow rate of the fuel-and-air mixture, improved combustion stability, an extremely compact construction and arrangement, a relatively simple design, extremely low cost when mass produced, and is rugged, durable, reliable, requires little maintenance and adjustment in use, and in service has a long useful life.